Method of manufacturing liquid crystal devices

ABSTRACT

An improved method for manufacturing liquid crystal devices is described. The method comprises mating a pair of substrates with an inner space therebetween, sealing the periphery of the mated substrates save for inlet ports, placing the mated substrates in a vacuum chamber, evacuating air from the inner space between the substrates by virtue of the differential pressure between the inner space and the vacuum chamber, pouring a liquid crystal material into the inlet ports, introducing the liquid crystal material into the inner space by elevating the pressure of the vacuum chamber at an elevated temperature, cooling the liquid crystal material, and closing the inlet ports by means of a sealing member. The removal of the superfluous portion of the liquid crystal material is done only after closing of the inlet ports.

BACKGROUND OF THE INVENTION

The present invention relates to a method of manufacturing liquidcrystal devices.

Liquid crystal displays have been broadly applied to personal computors,wordprocessors, and others. Liquid crystals mainly used in such devicesare twisted nematic type materials. On the other hands, liquid crystalmaterials exhibiting smectic A and chiral smectic C phases areattracting interest of researchers because of new type driving modes.

In case of smectic phases, it is likely that external force or impactslikely cause disturbance in molecular arrangement of the liquid crystal.Unevenness of the cell thickness produces color shade in the displaydriven in accordance with the birefringence mode. The provision ofspacers are used for fixing a pair of substrates at intermediatepositions in order to deal with the problems.

The distance between a pair of substrates have to be so chosen as tounwind molecular spirals formed in the chiral smectic C liquid crystallayer disposed between the substrates. In order to dispose a liquidcrystal material, the mated substrates are placed in a vacuum chamberand the pressure is reduced so that the air present in the inner spacebetween the substrates is evacuated therefrom. Then, after an amount ofthe liquid crystal material is poured to an inlet port provided at aprepheral position of the mated pair of substrates, the pressure in thevacuum chamber is elevated in order to introduce the liquid crystalmaterial into the inner space at an elevated temperature at which thephase of liquid crystal material exhibits a low coefficient ofviscosity. Finally, the inlet port is closed by a suitable sealingmaterial.

However, in accordance with this conventional method, void spaces may beproduced in the liquid crystal layer due to thermal contraction andtherefore the yield of product is substantially reduced.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method ofmanufacturing liquid crystal devices without causing void spaces in theliquid crystal layer between a pair of substrates.

It is another object of the present invention to provide a method ofmanufacturing liquid crystal devices which can be driven without causingcolor shade due to unevenness of the thickness of the liquid crystallayer interposed between the pair of substrates.

In order to accomplish the above and other objects, an amount of liquidcrystal material is introduced into the space between a pair of glasssubstrates through inlet ports, and the temperature is graduallydescended in advance of sealing off of the inlet ports. The coolingspeed is determined depending on the kind of the liquid crystal materialand the dimension of the inlet ports.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1(A) and 1(B) are perspective and cross sectional views of aliquid crystal device of intermediate production condition prior tointroduction of liquid crystal material in accordance with the presentinvention.

FIG. 2 is a perspective view showing a modification of the liquidcrystal device blank shown in FIGS. 1(A) and 1(B).

FIG. 3 is a plan view showing a temperature control device utilized inaccordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIGS. 1(A) and 1(B), a method of manufacturing a liquidcrystal device in accordance with the present invention is described.The device comprises a pair of glass substrates 9 and 10, a pair oftemperature electrode arrangements 15 formed in the inside surfaces ofthe substrates, a pair of orientation control films 16 formed on theopposed insides of the substrates 9 and 10, spacers 13 controlling thedistance between the substrates, adhesive resin members 12 fixing thesubstrates and a sealing member 11 provided on the periphery of thesubstrates for avoiding loss of liquid crystal material. A plurality ofinlet ports 14 are formed at the right edge of the substrate whereprovision of the sealing member is partially omitted. The orientationcontrol film is given rubbing treatmemt in the vertical direction asshown by an arrow. The orientation control films help homogeneousalignment of the liquid crystal molecules.

The liquid crystal device structure of such an intermediate productcondition is placed in a vacuum chamber and the pressure is reduced to6×10⁻³ Torr. Then, an amount of a C liquid crystal material is poured bymeans of a dispenser to close the inlet ports at an elevated temperatureat which the liquid crystal is in a nematic or isotropic phase. Thephase of the liquid crystal material is chiral smectic C at theoperation temperature of the device. In this condition, the pressure inthe vacuum chamber is returned to an atmospheric pressure in order tofill the space between the substrates with the liquid crystal materialby virtue of the differential pressure between the inside and theoutside of the liquid crystal device. The structure is then removed fromthe chamber and placed in a constant temperature bath with the liquidcrystal material remaining in the vicinity of the inlet ports as it is.The temperature of the structure is descended uniformly to 0° C. at acooling rate of -5° C./hour. After 0° C. is reached, an ultravioletcurable epoxy resin adhesive is applied to the inlet ports in order toclose them followed by eliminating the liquid crystal material presentoutside of the device. Crossed Nicols may be provided on the externalsurfaces of the structure if necessaty. Alternatively, the inlet portsmay be formed not only at the right side but also at the left side asshown in FIG. 2.

The cooling operation of the structure can be performed by use of anapparatus illustrated in FIG. 3. The apparatus comprises a plurality ofconstant temperature plates 17, the temperatures of which are elevatedfrom the leftest plate to the rightest plate. The structre as shown inFIGS. 1(A) and 1(B) and containing the liquid crystal material thereinis mounted on the apparatus and conveyed to the right direction (to thetemperature rising direction) with the inlet ports at the head. Afterthe temperature of the liquid crystal falls to 0° C., the inlet port issealed off as previously described.

While several embodiments have been specifically described, it is to beappreciated that the present invention is not limeted to the particularexamples described and that modifications and variations can be madewithout departure from the scope of the invention as defined by theappend claims.

I claim:
 1. A method of disposing a liquid crystal material between apair of substrate comprising:forming an electrode arrangement on theinside surfaces of a pair of substrates; coating an orientation controlfilm on the inside surface of at least one of said substrates; givingorientation treatment to said orientation control film; mating said pairof substrates with an inner space therebetween; sealing the periphery ofthe mated substrates except for at least one inlet port, said inlet portbeing aligned so that a fluid can flow into said inner space in thedirection approximately perpendicular to the direction of saidorientation treatment; placing the sealed substrates in a vacuumchamber; descending the pressure in said vacuum chamber; pouring saidliquid crystal material into said inlet port at an elevated temperatureat which said liquid crystal material exhibits a low viscosity;elevating the pressure in said vacuum chamber in order to introduce saidliquid crystal material onto said inner space; descending thetemperature of said liquid crystal material between said substrates tothe operable level at which said liquid crystal material exhibits a highviscosity, with the liquid crystal material being present in thevicinity, said temperature descending including descending the liquidcrystal temperature to approximately 0° C. or below; sealing off saidinlet port in order to avoid loss of said liquid crystal materialcontained in the inner space, said sealing occurring while said liquidcrystal is substantially at the descended temperature; and removing theremaining portion of said liquid crystal material from the vicinity ofsaid inlet port.
 2. The method of claim 1 wherein said liquid crystalmaterial is chiral smectic C at the operation temperature of said liquidcrystal device.
 3. The method of claim 2 wherein said temperaturedescending step is carried out uniformly throughout said space.
 4. Themethod of claim 2 wherein said inlet port is formed on the one edge ofsaid pair of substrates, and the temperature of the liquid crystalmaterial contained in said space is descended in the manner that thetemperature in the vicinity of said inlet port is higher than that inthe opposed side.
 5. The method of claim 4 wherein said temperaturedescending step is carried out by use of a plurality of constanttemperature plates whose temperatures range from a higher temperature toa low temperature and over which said substates is conveyed in order tobe gradually cooled.